In a typical manual “pull-down” band saw the force at which the band saw blade is fed into the work piece is not mechanically controlled, but rather is provided manually by the operator. As a result, the feed force is limited and can vary depending on the physical strength and ability of the operator. Such pull-down band saws can be used to cut metal work pieces including, for example, roll formed, structural shapes, such as metal pipes, fence posts, and other metal work pieces defining unique or odd shaped profiles. The band saw blades used for such applications are typically bi-metal with flexible, spring steel backings, and cutting teeth with tool steel tips that are welded to the spring steel backings. Due to the relatively uncontrolled nature of the feed force in manual pull-down band saws, relatively high impact cutting forces can be imparted to the cutting teeth, particularly when cutting metal, structural work pieces. As a result, a primary failure mode of band saw blades used in such applications is tooth damage due to chipping at the tool steel tips and/or stripping of the teeth away from the band at the bi-metal weld region or interface.
One of the drawbacks of prior art band saw blades used in such applications is that the blades fail prematurely, particularly as a result of the above-mentioned tooth chipping and/or stripping, and therefore the blades do not provide as long a blade life as desired. Another drawback is that the band saw blades do not use the manually-supplied feed forces as efficiently as desired, and as a result, the time required to cut through work pieces can be longer than desired. Commercially available band saw blades utilize a variety of methodologies to provide more robust tooth forms and thereby increase blade life. A first methodology utilizes neutral or relatively small rake angles to maximize the included angle between the rake face and clearance surfaces of the teeth. A second methodology utilizes a somewhat reduced primary clearance angle in conjunction with a larger secondary clearance angle to maximize the included angle. A third methodology utilizes a significantly reduced primary clearance angle in conjunction with a larger secondary clearance angle to maximize the included angle.
The present inventor has determined that these methodologies have achieved varying and limited levels of effectiveness. The first methodology can cause the cutting to be less efficient than desired while allowing for only relatively minimal gains in resisting tooth strippage. The second methodology, on the other hand, can be more effective at reducing tooth strippage, but can require longer cutting times than desired. The third methodology also can be effective at reducing tooth stripping and chipping, but the tooth form defines relatively small gullets that become more easily filled with chips. This can reduce the rate at which the band saw is fed into the work piece, can cause the blade to stall and/or can lead to crooked cutting.
It is an object of the present invention to overcome one or more of the above-described drawbacks and/or disadvantages of the prior art.